The interplay of normal and pathological biology that characterizes research on Alzheimer's disease is particularly well illustrated by studies of two proteins that have been directly implicated in the genetic mechanisms of AD: the presenilins (PS) and the beta-amyloid precursor protein (APP). In this Program Project grant, four independent laboratories that have each contributed productively over many years to the elucidation of the mechanisms of AD are joining forces to apply a wide range of techniques in a molecular and cell biology, neuropathology and animal modeling to address key unresolved questions about the presenilins and their role in AD pathogenesis. The central vision of our Program is to use the combined expertise of these four well-established laboratories and their extensive array of techniques and reagents they possess to examine in detail the biology of the presenilins, their interactions with other functionally important neuronal proteins (including APP, Notch and the catenins and their pathogenic role in the most common and aggressive form of genetically based AD. The principal investigators, who have collaborated on numerous occasions in the past, have been meeting together regularly for many months to discuss scientific questions of mutual interest, share unpublished data, exchange reagents, cross-validate findings and design new collaborative experiments, the most compelling of which have been incorporated into this Program. Among our numerous Specific Aims (organized into 4 projects), we will: 1) characterize in detail cellular and subcellular anatomy of PS1 in our transgenic mice expressing wt versus mutant PS1, using in situ hybridization and confocal microscopy with newly developed reagents; 2) assess AD-like pathology in these mice and new mice resulting from crossing our mice with PDAPP V717F transgenic mice, using modern quantitative stereology; 3) examine the complex endoproteolysis of PS, including an exciting novel apoptotic pathway we have recently identified, and how this is changed by PS mutations, but in cells and in transgenic mice; 4) use the PS mutations as a route to defining the elusive mechanism of gamma-secretase processing of APP, in view of the highly selective effect of mutant PS on Abeta42 production and our recent demonstration of a direct interaction of APP with both PS1 and PS2 in the ER and Golgi; and 5) characterize the cell biology of a novel member of the catenin family we recently cloned as a PS-interaction in vivo and assess how it functions in cell signaling and whether it participates in the PS-APP complexes. These are but a few of the unanswered questions about the structure and function of the presenilins we will approach. Our experiments will be supported by 3 Cores, including one for breeding and maintaining transgenic mice, and one that will characterize and distribute a very large array of DNA constructs, stable cell lines, probes and antibodies and will conduct sensitive Abeta ELISAs. Our proposed experiments are hypothesis-driven and, in each case, based on strong preliminary data. We believe our combined experiences and our committed group of senior and junior scientists will enable us to successfully execute a highly integrated program of basic and applied molecular neurobiology that will have direct implications for understanding the mechanism and treatment of AD.